Multi-layered ceramic enclosure

ABSTRACT

Techniques for fabricating a laminated ceramic housing that can be used for a handheld computing device that includes an enclosure having structural walls formed from a multi-layered ceramic material that can be radio-transparent. The multi-layered ceramic housing can be formed of a plurality of ceramic materials such as zirconia and alumina in any combination. The multi-layer ceramic substrate includes an inner layer and surface layers that sandwich the inner layer. The multi-layer ceramic substrate has an increased transverse strength due to the surface layers having a coefficient of thermal expansion (CTE) that is less than that of the inner layer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The described embodiments relate generally to portable computingdevices. More particularly, the present embodiments relate to enclosuresof portable computing devices.

2. Description of the Related Art

In recent years, portable electronic devices, such as laptop computers,tablet computers, PDAs, media players, and cellular phones, have becomecompact and lightweight yet powerful. As manufacturers have been able tofabricate various operational components of these devices in smallersizes, the devices themselves have become smaller. In most cases,despite having a more compact size, such components have increased poweras well as operating speed. Thus, smaller devices may have much morefunctionality and power than larger devices of the past.

One design challenge is to provide an aesthetically pleasing enclosurethat is functional for the intended purpose of the device. With moredevices being capable of wireless communications, a radio transparentenclosure would be beneficial, as it would allow components, such asantennas, to be positioned inside the enclosure. Users also desire anenclosure that can withstand mishaps. Thus, a water-resistant andscratch-resistant enclosure would also be desirable.

Therefore, it would be beneficial to provide improved enclosures forportable computing devices, particularly enclosures that are functionaland aesthetically pleasing yet durable.

SUMMARY OF THE DESCRIBED EMBODIMENTS

This paper describes various embodiments that relate to systems,methods, and apparatus for providing an enclosure suitable for aportable computing device. In particular, the enclosure is formed of aceramic laminate. The ceramic laminate is formed of a plurality oflayers of ceramic material where at least two adjoining layers havediffering properties. In one embodiment, the adjoining layers can havedifferent coefficients of thermal expansion (CTE) such that an outerlayer has compressive residual stress and an inner portion sandwichedbetween at least two other layers with compressive stress profiles has atensile residual stress profile.

According to one embodiment, a multi-layer ceramic housing arranged forenclosing operational components of a portable electronic device isdescribed. The multi-layered ceramic housing includes at least a ceramiclaminate structure. The ceramic laminate structure includes an innerlayer and a first and second outer layer each in contact with a least aportion of the inner layer, the inner layer being arranged between thefirst and second outer layer in a stacked arrangement. The first andsecond outer layers have a CTE that is less than the inner layer, andwherein the first and second layers have a compressive residual stressprofile and the inner layer has a tensile residual stress profile.

According to another embodiment, a method for forming a multi-layerceramic substrate is described. The method is performed by carrying outthe following operations: providing a first layer of ceramic materialhaving a first binder loading, providing a second layer of ceramicmaterial having a second binder loading, and processing the first andsecond layers of ceramic material to form the multi-layer ceramicsubstrate, wherein the first layer forms a top portion and bottomportion of the multi-layer ceramic and the second layer forms aninterior portion of the multi-layer ceramic substrate sandwiched betweenthe top and bottom portions. The top and bottom portions each have acompressive residual stress profile and wherein the inner portion has atensile residual stress profile.

According to yet another embodiment, an apparatus for forming amulti-layer ceramic substrate is described. In one embodiment, theapparatus includes at least means for providing a first layer of ceramicmaterial having a first binder loading, means for providing a secondlayer of ceramic material having a second binder loading, means forprocessing the first and second layers of ceramic material to form themulti-layer ceramic substrate, wherein the first layer forms a topportion and bottom portion of the multi-layer ceramic and the secondlayer forms an interior portion of the multi-layer ceramic substratesandwiched between the top and bottom portions. The top and bottomportions each have a compressive residual stress profile and wherein theinner portion has a tensile residual stress profile.

Other aspects and advantages of the invention will become apparent fromthe following detailed description taken in conjunction with theaccompanying drawings which illustrate, by way of example, theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be readily understood by the following detaileddescription in conjunction with the accompanying drawings, wherein likereference numerals designate like structural elements, and in which:

FIG. 1 is an exploded perspective diagram of an electronic device, inaccordance with one embodiment.

FIG. 2 shows a representation cross section of housing as one embodimentof housing shown in FIG. 1 in accordance with the described embodiments.

FIGS. 3A and 3B show representative residual stress profiles for aceramic laminate (stepped profile in FIG. 3A) and conventional glass(parabolic profile in FIG. 3B).

FIG. 4 shows a flowchart detailing process in accordance with thedescribed embodiments

DETAILED DESCRIPTION OF SELECTED EMBODIMENTS

Reference will now be made in detail to representative embodimentsillustrated in the accompanying drawings. It should be understood thatthe following descriptions are not intended to limit the embodiments toone preferred embodiment. To the contrary, it is intended to coveralternatives, modifications, and equivalents as may be included withinthe spirit and scope of the described embodiments as defined by theappended claims.

Lamination of different thin ceramic layers to form thick substrates canbe considered a suitable solution to increase fracture toughness ofceramic materials. For the preparation of these composites warm pressingand sintering of ceramic layers can be used. Laminates with strongadhesion generate structure with residual stresses due to the mismatchin elastic modulus, shrinkage and coefficient of thermal expansion (CTE)among different layers. Such a residual stress gives rise to highervalues of strength, apparent toughness and wear resistance overmonolithic materials with the same composition In particular theobserved toughening mechanism can be related to residual stresses andcrack propagation. The stress profile of the laminated structure has astrong effect on the apparent fracture toughness of a laminatecomposite.

The embodiments described herein relate to using ceramic laminates inthe fabrication of a housing used to enclose and support operationalcomponents used for a portable electronic device. The housing is formedof multiple layers of ceramic materials arranged in such a way to formcompressive outer layers and tensile inner layer as evidenced by astress profile. In one embodiment, the multiple layers can be formed ofceramic materials along the lines of aluminum oxide (Al₂O₃), alsoreferred to as alumina, and known to be RF energy transparent and a goodelectrical insulator. Other ceramic materials considered includezirconium dioxide (Zr, Ti, Ca)O₂, also referred to as zirconia, known tohave superior mechanical properties, but is nonetheless, essentiallyopaque to RF energy transmission. Therefore, in those situations wherethe portable electronic device includes RF circuitry, it is advantageousto provide multiple layers of ceramic material that when taken togetherprovides a housing that is both mechanically resilient and suitably RFenergy transparent.

Accordingly, the embodiments described relate to a multi-layered ceramicstructure used to enclose and support various operational components fora portable handheld electronic device having RF capabilities such asWiFi and cellular telephony. The multi-layered ceramic structureincludes a first and second outer layer formed of a ceramic materialsuitably configured for providing good resistance to externally appliedstress and other environmental affronts. In one embodiment, the outerlayers can be formed of, for example, Zirconia, using any availableceramic fabrication process such as a doctor blade process in which asharp blade is used in combination with a ceramic slurry to apply a thinlayer of ceramic material on a roller assembly to form thin sheets ofceramic material. Other techniques well known in the art of ceramicfabrication includes at least ceramic injection molding (CIM); lowtemperature co-fired ceramic (LTCC), tape casting and so on.

In any case, the thin sheets of ceramic material can be infused withvarying amounts and size of binding material (generally organic materialsuch as wax, plastic, etc.) in order to adjust an amount of shrinkage ofthe thin ceramic sheets during a firing process in which the bindingmaterial is burned off. For example, by infusing the thin ceramic sheetswith a higher binder loading, the more extensive the shrinkage of thelayer and the more compressive stress profile will be generated in thelayer. Alternatively, by providing a lower binder loading, the amount ofshrinkage is commensurably reduced providing a more tensile stressprofile. In this way, by modifying the relative shrinkage in each layer,a specific stress profile can be created. The specific stress profilecan, for example, be associated with a compressive stress on exposedsurfaces and be associated with tensile stress within interior regionscoupled to the compressive surface regions.

These and other embodiments are discussed below with reference to FIG.1-xx. However, those skilled in the art will readily appreciate that thedetailed description given herein with respect to these figures is forexplanatory purposes only and should not be construed as limiting.

FIG. 1 is an exploded perspective diagram of an electronic device 50, inaccordance with one embodiment. The device 50 may be sized forone-handed operation and placement into small areas, such as a pocket.In other words, the device 50 can be a handheld pocket-sized electronicdevice. By way of example, the electronic device 50 may correspond to acomputer, media device, telecommunication device, and the like. Thedevice 50 includes a housing 52 that encloses and supports internallyvarious electrical components (including, for example, integratedcircuit chips and other circuitry) to provide computing operations forthe device 50. The housing 52 can also define the shape or form of thedevice 50. That is, the contour of the housing 52 may embody the outwardphysical appearance of the device 50. It should be noted that, althoughthe device 50 is illustrated in FIG. 1 with 90 degree edges, it will beunderstood that the device 50 can have rounded or chamfered edges.

The housing 52 generally includes a main integral body 54. By integral,it is meant that the main body is a single complete unit. By beingintegrally formed, the main body is structurally stiffer thanconventional housings, which typically include two parts that arefastened together. Furthermore, unlike conventional housings that have aseam between the two parts, the main body has a substantially seamlessappearance. Moreover, the seamless housing prevents contamination and ismore water resistant than conventional housings. The main body 54 canalso include one or more windows 56, which provide access to theelectrical components, particularly the user interface elements, whenthey are assembled inside the cavity 58 of the main body 54. In thedescribed embodiment, the main body 54 may be formed from a variety ofceramic materials. In a particular embodiment, the main body is formedof a plurality of ceramic materials combined in a layer likearrangement. In one embodiment, the layers of ceramic material can bedifferent. For example, an inner layer can be formed of a first ceramicmaterial sandwiched between at least two outer layers. In oneimplementation, the ceramic materials can be the same but have differentproperties.

The ceramic material selected generally depends on many factorsincluding, but not limited to, strength (tensile), density(lightweight), strength to weight ratio, Young's modulus, corrosionresistance, formability, finishing, recyclability, tooling costs, designflexibility, manufacturing costs, manufacturing throughput,reproducibility, and the like. The material selected may also depend onelectrical conductivity, thermal conductivity, radio wave transparency,combustibility, toxicity, and the like. The material selected may alsodepend on aesthetics, including color, surface finish, and weight.

For example, if it is desired that the housing 52 be RF transparent,then the main body 54 can be formed of layers of ceramic material (suchas alumina) having the desired RF transparency. However, in order toassure that the housing 52 is resistant to external forces, the outerlayers of the housing 52 can be formed of alumina having been formedusing a high binder loading providing a more compressive residual stressthan those internal layers sandwiched between the outer layers where theinner layers have a lower binder loading providing a more tensileresidual stress. In this way, the outer layers provide a more resistantand resilient surface for the housing 52.

However, in order to optimize the properties of housing 52, it may beadvantageous to provide layers of different ceramic materials. Forexample, although alumina has good RF transmission properties, thestrength of, for example, zirconia can be better suited for applicationssuch as portable media players where housing 52 would be exposed tosubstantial mechanical, chemical, and other environmental impacts. Inthis case, the outer layers of the housing 52 can be formed of, forexample, zirconia, having a residual compressive stress profile thatsandwiches an internal layer of alumina providing a good RF transmissioncapability. For many of the reasons above, the housing 52 can be formedof multi-layered (i.e., laminated) ceramic materials that are strong,stiff, and radio transparent and therefore a suitable material for anenclosure of an electronic device capable of wireless communications.The radio transparency is especially important for wireless hand helddevices that include antennas internal to the enclosure. Radiotransparency allows the wireless signals to pass through the enclosureand, in some cases, even enhances these transmissions.

As discussed in more detail below, the laminated ceramic material can beformed so that the enclosure can have a seamless or substantiallyseamless appearance. The seamless enclosure, in addition to beingaesthetically pleasing, can provide the added benefit of lesscontamination and moisture intrusion into the interior of the device. Insome embodiments, the main body 54 can have a wall having a continuousuniform thickness all around. In other embodiments, however, the wall ofthe main body 54 can be thicker at the edge or corner portions toprovide strength in the areas where strength is more needed.

FIG. 2 shows a representation cross section of housing 200 as oneembodiment of housing 52 shown in FIG. 1 in accordance with thedescribed embodiments. The cross sectional view of housing 200 providesone example of a laminated ceramic structure that can be used to providehousing 200 with the properties appropriate for the electronic devicefor which it is intended. For example, layer 202 can be formed of aceramic material (such as zirconia). In order to provide layer 202 witha relatively compressive stress profile, layers 202 can be fabricated inusing a high binder loading as compared to layer 204 sandwiched therebetween having been fabricated with a lower binder loading. In this way,a composite residual stress profile as shown in FIG. 3A can be providedshowing a stepped residual stress profile. By stepped residual stressprofile, it can be seen that the residual stress in both layers 202 arecompressive whereas the residual stress is tensile in layer 204. Thestepped nature of the laminate structure differs markedly from the moreGaussian shape associated with, for example, hardened glass shown forcomparison on FIG. 3B.

Another benefit of using a multi-layer ceramic is that the enclosure canbe made stronger if the housing includes multiple layers havingdifferent coefficients of thermal expansion (CTE). If the external layerhas a high CTE and the internal layer has a low CTE, then the two layers202, 204 will fuse into one layer, with the external surface layer 202being in a compressive state. The skilled artisan will appreciate thatceramic material is stronger in compression and weaker in tension, andthe different binder loadings will result in the external surface layer202 being in compression and therefore stronger.

FIG. 4 shows a flowchart detailing process 400 in accordance with thedescribed embodiments. Process 400 can be used to form a ceramiclaminate structure. The ceramic laminate structure can be used toenclose operational components used in the assembly of a portableelectronic device. The ceramic laminate structure can take the form ofhousing. In those cases where the portable electronic device utilizes RFcircuits, the ceramic laminate structure can be formed of a combinationof ceramic materials some of which provide good mechanical propertiesand resistance to environmental affront and other ceramic materials thatprovide good RF transmissivity. In this way, an optimal arrangement ofceramic layers can be provided that are customized for a particularfunctionality of the portable electronic device.

Process 400 can be performed by providing a first layer of ceramicmaterial at 402. In one embodiment, the first layer of ceramic materialcan be arranged to have a tensile residual stress profile. This can beaccomplished by controlling an amount of shrinkage during a firingprocess. The amount of shrinkage can be controlled by adjusting a binderloading in the ceramic material. A higher binder loading can cause theceramic material to undergo relatively more shrinkage. Alternatively, alower binder loading can result in less shrinkage and therefore a moretensile residual stress. At 404, the first layer is associated with afirst binder loading. For example, if the first layer is determined tobe associated with an exterior surface, than the first binder loading isassociated with a high binder loading. Next at 406, a second layer ofceramic material is provided. The second layer of ceramic material isthen associated with a second binder loading at 408. As with the firstlayer, the second binder load is dependent upon the function to beperformed by the second layer. For example, if the second layer isdetermined to form the body of a housing that must be RF transparent,then the ceramic material of the second layer can be different than theceramic material that forms the first layer. Moreover, the difference inbinding loadings between the first and second layers can be associatedwith a residual stress profile that limits damage caused by externalimpacts, and so forth. At 410, the first and second ceramic layers areprocessed to form a ceramic laminate in accordance with the first andsecond binder loading. In one embodiment, the ceramic laminate bystacking the first and second layers and then firing the stacked layers.

Moreover, although not shown, the various components of the enclosuremay consist of multiple layers that are glued, press fit, molded orotherwise secured together. In one example, the enclosure consists ofmultiple layers that form a single laminate structure formed for exampleby gluing. By way of example, the entire or portions of the enclosurewalls may be formed from layers of metals, ceramics and/or plastics. Inthe case of radio transparency, the layers may include glass andceramics as, for example, forming a wall with a glass outer layer and aceramic inner layer (or vice versa).

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and equivalents, whichfall within the scope of this invention. For example, although someembodiments include an integrally formed internal rail system, in somecases the internal rail system may be a separate component that isattached within the main body or it may not even be included in somecases. It should also be noted that there are many alternative ways ofimplementing the methods and apparatuses of the present invention. Forexample, although an extrusion process is preferred method ofmanufacturing the integral tube, it should be noted that this is not alimitation and that other manufacturing methods may be used in somecases (e.g., injection molding, press forming). In addition, althoughthe invention is directed primarily at portable electronic devices suchas media players, and mobile phones, it should be appreciated that thetechnologies disclosed herein can also be applied to other electronicdevices, such as remote controls, mice, keyboards, monitors, andaccessories for such devices. It is therefore intended that thefollowing appended claims be interpreted as including all suchalterations, permutations, and equivalents as fall within the truespirit and scope of the present invention.

What is claimed is:
 1. A multi-layer ceramic housing arranged forenclosing operational components of a portable electronic device,comprising: a ceramic laminate structure comprising: an inner layer, afirst and second outer layer each in contact with a least a portion ofthe inner layer, the inner layer being arranged between the first andsecond outer layer in a stacked arrangement, wherein the first andsecond outer layers have a CTE that is less than the inner layer, andwherein the first and second layers have a compressive residual stressprofile and wherein the inner layer has a tensile residual stressprofile.
 2. The multi-layer ceramic housing as recited in claim 1,wherein the first and second outer layers are formed of a first ceramicmaterial.
 3. The multi-layer ceramic housing as recited in claim 2,wherein the inner layer is formed of a second ceramic material.
 4. Themulti-layer ceramic housing as recited in claim 3, wherein the firstceramic material is zirconium dioxide.
 5. The multi-layer ceramichousing as recited in claim 4, wherein the second ceramic material isaluminum dioxide.
 6. A method for forming a multi-layer ceramicsubstrate, comprising providing a first layer of ceramic material havinga first binder loading; providing a second layer of ceramic materialhaving a second binder loading; processing the first and second layersof ceramic material to form the multi-layer ceramic substrate, whereinthe first layer forms a top portion and bottom portion of themulti-layer ceramic and the second layer forms an interior portion ofthe multi-layer ceramic substrate sandwiched between the top and bottomportions, wherein the top and bottom portions each have a compressiveresidual stress profile and wherein the inner portion has a tensileresidual stress profile.
 7. The method as recited in claim 6, whereinthe top and bottom portions each have a CTE that is less than the innerportion.
 8. The method as recited in claim 6, wherein the first andsecond outer layers are formed of a first ceramic material.
 9. Themethod as recited in claim 7, wherein the inner layer is formed of asecond ceramic material.
 10. The method as recited in claim 9, whereinthe first ceramic material is zirconium dioxide.
 11. The method asrecited in claim 4, wherein the second ceramic material is aluminumdioxide.
 12. An apparatus for forming a multi-layer ceramic substrate,comprising: means for providing a first layer of ceramic material havinga first binder loading; means for providing a second layer of ceramicmaterial having a second binder loading; means for processing the firstand second layers of ceramic material to form the multi-layer ceramicsubstrate, wherein the first layer forms a top portion and bottomportion of the multi-layer ceramic and the second layer forms aninterior portion of the multi-layer ceramic substrate sandwiched betweenthe top and bottom portions, wherein the top and bottom portions eachhave a compressive residual stress profile and wherein the inner portionhas a tensile residual stress profile.
 13. The apparatus as recited inclaim 12, wherein the top and bottom portions each have a CTE that isless than the inner portion.
 14. The apparatus as recited in claim 13,wherein the first and second outer layers are formed of a first ceramicmaterial.
 15. The apparatus as recited in claim 14, wherein the innerlayer is formed of a second ceramic material.
 16. The apparatus asrecited in claim 15, wherein the first ceramic material is zirconiumdioxide.
 17. The apparatus as recited in claim 16, wherein the secondceramic material is aluminum dioxide.